Trailing underscores on C function names

Trailing underscores on C function names

In the fastmatch package, version 1.1-0, there is a C function called
"ctapply_", with a trailing underscore. However, the NAMESPACE's call to
useDynLib refers to "ctapply", without the trailing underscore.

"Writing R Extensions" mentions, section 5.2, footnote 121, that .C and
.Fortran interpret their first argument as the name of the object file
symbol "possibly after some platform-specific translation, e.g. adding
leading or trailing underscores".

Should useDynLib use the underscored name? The code doesn't seem
"platform-specific". What are the rules concerning added underscores (or
capitalization?) that R uses?